Grinding apparatus and method for manufacturing magnetic recording medium using the same

ABSTRACT

A grindstone of a diamond wheel is cleaned by a rotating brush additionally provided in close proximity of the diamond wheel during a grinding operation in which a magnetic layer of a magnetic tape material being transferred is ground continuously by the diamond wheel.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a grinding apparatus and amethod for manufacturing a magnetic recording medium using the saidapparatus. More particularly, it relates to a grinding apparatussuitable for manufacturing a low-noise and high-density magneticrecording medium and a method for manufacturing a magnetic recordingmedium using the said apparatus.

[0003] 2. Description of the Related Art

[0004] Magnetic tapes made by applying a magnetic paint containingferromagnetic powder and a binder have been used widely as magneticrecording media for audio and video systems, broadcasting, computerbackup, and the like. In manufacturing such magnetic tapes, minuteprotrusions etc. on the surface of magnetic layer are sometimes removedby applying a grinding wheel such as a diamond wheel to the magneticlayer of magnetic tape (grinding) for prevention of wear of magnetichead, restraint of dropout, reduction in error rate, etc. (for example,Japanese Patent Application Publication No. 62-172532).

[0005] To manufacture such magnetic tapes, an apparatus is used whichhas a configuration such that a wide band-shaped magnetic tape materialwound in a roll shape is cut into a plurality of narrow magnetic tapeswith a slitter while being transferred, the magnetic tape is ground by agrinding wheel such as a diamond wheel, and subsequently the magnetictape is wound up into a roll shape.

[0006]FIG. 6 is a schematic view in which the surfaces of magneticlayers of magnetic tapes 1, 1 . . . are ground by a grinding wheel 2.Conventionally, the grinding operation has been performed by windinglyapplying a plurality of (for example, forty) magnetic tapes 1, 1 . . .with a predetermined width (for example, 12.65 mm in width) to thecylindrical grinding wheel 2 having a predetermined length (for example,1 m) as shown in FIG. 6.

[0007] However, such a grinding operation has a problem in that thegrinding force of the grinding wheel 2 decreases gradually. The causefor this phenomenon of decreased grinding force is thought to be loadingof grindstone caused by additives such as a binder component of magneticlayer, transferred objects of back layer, chips produced when themagnetic tape material is cut, shavings removed by grinding, and thelike. If loading of grindstone occurs, the grinding force of grindingwheel for grinding the magnetic layer becomes nonuniform, and thequality of manufactured magnetic tape becomes unstable. In particular,in the case where the band-shaped magnetic tapes being transferred areground continuously, a variation in the grinding force of grinding wheelcauses a problem of the quality of magnetic tape that varies in thetransfer direction of magnetic tape.

[0008] As a solution to this problem, conventionally, when loading ofthe grindstone of grinding wheel occurs, the grindstone surface is wipedoff with a cloth etc. soaked with a solvent etc. capable of dissolvingthe magnetic paint to eliminate the loading of grindstone. This methodhas achieved a degree of effect.

SUMMARY OF THE INVENTION

[0009] However, in the above-described conventional method, the loadingof grindstone occurs frequently, and on all such occasions, in order torestore the grinding force of grindstone, work is needed to wipe thegrindstone surface with a cloth soaked with a solvent etc. by temporallystopping the production line for magnetic recording medium, whichsignificantly deteriorates the productivity because of a burden onworker, an increase in downtime, and the like. Also, the loading ofgrindstone cannot often be eliminated by such work.

[0010] Also, as drastic measures against the loading of grindstone, thedressing of the grinding wheel is effective. However, when the dressingwork is entrusted to the wheel manufacturer or the like, there arises aproblem of long delivery time and high cost. Also, the productivity isdeteriorated significantly by increased downtime and the like.

[0011] An object of the present invention is to provide a grindingapparatus capable of manufacturing a high-quality magnetic recordingmedium with low noise and high density stably with a high rate ofoperation by stabilizing the grinding force of a grinding wheel, and amethod for manufacturing a magnetic recording medium using the grindingapparatus.

[0012] To achieve the above object, the present invention provides agrinding apparatus including a grinding wheel which continuously grindsthe surface of a running web; and a cleaning device additionallyprovided in close proximity of the grinding wheel, which cleans agrindstone of the grinding wheel.

[0013] According to the grinding apparatus in accordance with thepresent invention, since the grindstone of the grinding wheel can becleaned by the cleaning device during the grinding operation of the web,the loading of the grindstone can be eliminated effectively. Thereby,the grinding force of the grindstone of the grinding wheel can bestabilized, so that the variations in quality of the web in the webtransfer direction can be prevented. Therefore, the grinding apparatusin accordance with the present invention is suitable as a grindingapparatus used in a method for manufacturing a magnetic recordingmedium, in which a transferred band-shaped magnetic recording mediummust be ground continuously by the grinding wheel and the grindingeffect in the transfer direction of the magnetic recording medium mustbe uniformed, like the grinding operation of a magnetic layer of themagnetic recording medium.

[0014] Also, in the grinding apparatus in accordance with the presentinvention, the cleaning device is preferably a rotating brush having agreat effect of cleaning the grindstone of the grinding wheel. Thereason for this is that the decrease in grinding force of the grindstoneof the grinding wheel is caused by the adhesion of loaded substances toabrasive grains of the grindstone or the intrusion thereof into concaveportions, and it can be anticipated that the brush of the rotating brushnot only removes the loaded substances adhering to the abrasive grainsbut also scrapes off the loaded substances from the concave portions. Inparticular, the rotating brush is effective as a cleaning device whichremoves the loaded substances in the grinding wheel for grinding themagnetic recording medium.

[0015] Also, to achieve the above object, the present invention providesa method for manufacturing a magnetic recording medium, including thesteps of applying a magnetic paint containing ferromagnetic powder and abinder onto a nonmagnetic band-shaped flexible base material to betransferred to form a magnetic layer; and grinding the magnetic layercontinuously with a grinding wheel on the downstream side of transfer,wherein a cleaning device which cleans a grindstone of the grindingwheel is additionally provided in close proximity of the grinding wheelto clean the grindstone during the grinding operation.

[0016] According to the method for manufacturing a magnetic recordingmedium in accordance with the present invention, the grindstone of thegrinding wheel is cleaned by the cleaning device additionally providedon the grinding wheel during the grinding operation in which themagnetic layer of transferred magnetic recording medium is ground by thegrinding wheel. Therefore, the loading of grindstone of the grindingwheel can be eliminated effectively. Thereby, the grinding force of thegrinding wheel can be stabilized, so that a high-quality product of alow-noise and high-density coating type magnetic recording medium can bemanufactured stably. Further, there is no need for stopping themanufacture of magnetic recording medium to clean the grindstone of thegrinding wheel, so that the magnetic recording medium can bemanufactured with a high rate of operation.

[0017] According to the present invention, it is preferable that thegrindstone of the grinding wheel be always cleaned by the cleaningdevice during the time when the magnetic layer is ground by the grindingwheel. Thereby, the grinding force of the grinding wheel can be keptconstant, being almost the same as the initial grinding force, so that ahigher-quality magnetic recording medium having no variations in qualitycan be manufactured.

[0018] The present invention is not limited to the above-describedconfiguration in which the grindstone is always cleaned during thegrinding operation of the magnetic layer. The grindstone may be cleanedintermittently during the grinding operation of the magnetic layer.Further, the grindstone may be cleaned during the time when one roll(bulk) for manufacturing the magnetic recording medium is changed to thenext roll. In this case as well, a degree of effect of restoring thegrinding force of grindstone can be achieved.

[0019] In the present invention, the cleaning device is preferably arotating brush for brushing the grindstone. The reason for this is thesame as the reason explained regarding the grinding apparatus.

[0020] In the present invention, the brush material of the rotatingbrush is preferably one of chemical fiber, animal fiber, and vegetablefiber. A brush other than the above-described fibers, for example, ametal brush has a problem in that it easily damages the grindstone, andhence the abrasive grains rather come off from the grindstone. Among thechemical fiber, animal fiber, and vegetable fiber, the chemical fiber isexcellent in wear resistance and heat resistance (resistance to heatgenerated by the rotation of rotating brush), and thus it is suitable asthe brush of the rotating brush. As the chemical fiber, nylon, acrylic,Teflon, etc. are suitable. Also, a brush produced by mixing a fillersuch as aluminum oxide with the chemical fiber is especially preferred.

[0021] In the present invention, it is preferable that the rotationalspeed of the rotating brush be in the range of 100 to 1000 rpm, thebrush bristle diameter of the rotating brush be in the range of 0.01 to0.3 mm, and the brush bristle length of the rotating brush be in therange of 5 to 30 mm. Also, it is preferable that the brush of therotating brush be pressed against the grindstone of the grinding wheelunder a pressure such that the amount of pressing of the brush againstthe grindstone is in the range of 1 to 5 mm. If these conditions aremet, an especially great cleaning effect can be achieved. Herein, theamount of pressing means a distance through which the rotating brush isbrought close to the grinding wheel from a state in which the tip end ofbrush of the rotating brush is in contact with the grindstone surface ofthe grinding wheel in a straight form. By pressing the brush against thegrindstone with the amount of pressing being provided, the brush comesinto contact with the grindstone in a state in which the tip end portionthereof is defected.

[0022] Also, in the present invention, it is preferable that therotating brush be covered with a suction hood having an opening on thegrinding wheel side, and the suction pressure in the suction hood be 1to 5 kPa. Thereby, the loaded substances having removed from thegrinding wheel can be prevented from adhering to the magnetic recordingmedium.

[0023] As described above, according to the grinding apparatus and themethod for manufacturing a magnetic recording medium using the apparatusin accordance with the present invention, loaded substances such asadditives such as a binder component of magnetic layer causing loadingof grinding wheel, transferred objects of back layer, chips producedwhen a magnetic tape material is cut, and the like can be removedeffectively by the cleaning device in the grinding process. Thereby, thegrinding force of the grinding wheel is stabilized, so that ahigh-quality product of a low-noise and high-density coating typemagnetic recording medium can be manufactured stably with a high rate ofoperation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a schematic view of a magnetic tape manufacturing systemwhich is used in the present invention;

[0025]FIG. 2 is a side view of a slitter;

[0026]FIG. 3 is a schematic view of a grinding apparatus in accordancewith the present invention;

[0027]FIG. 4 is a conceptual view showing a configuration of an abrasiontest;

[0028]FIGS. 5A to 5C are graphs showing the results of abrasion test;and

[0029]FIG. 6 is a conceptual view showing a state in which a grindingoperation is performed using a conventional diamond wheel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Preferred embodiments of a grinding apparatus in accordance withthe present invention and a method for manufacturing a magneticrecording medium using the apparatus will now be described in detail.

[0031]FIG. 1 is a schematic view showing one example of a manufacturingsystem 10 for a magnetic tape (magnetic recording medium), to which themethod for manufacturing a magnetic recording medium in accordance withthe present invention is applied.

[0032] The magnetic tape manufacturing system 10 shown in FIG. 1includes a tape supply device 13 which sends out a wide web-shapedmagnetic tape material 20 wound in a roll shape, a slitter (cuttingapparatus) 14 which cuts the wide magnetic tape material 20 into aplurality of narrow magnetic tapes 26, a grinding apparatus 80 with acleaning device, which winds and grinds the magnetic tapes 26, and atape winding-up device 50 which winds up the magnetic tapes 26individually around a hub 18 (core) of a winding-up reel 17.

[0033] On a hub 12 (core) of a supply reel 11 in the tape supply device13, the magnetic tape material 20 wound in a roll shape is mounted.

[0034] The magnetic tape material 20 is usually manufactured by forminga magnetic layer by applying a magnetic paint containing ferromagneticparticulates to a nonmagnetic flexible base material and by subjectingthe magnetic layer to surface treatment such as orientation, drying,calendering (smoothening of magnetic layer), and hardening. To form themagnetic layer, besides the coating treatment, the vacuum depositionmethod or the like can be used.

[0035] As the nonmagnetic band-shaped flexible base material, generally,a flexible band-shaped object having a predetermined width, a length of45 to 20,000 m, and a thickness of 2 to 200 μm, or a band-shaped objectin which a fabrication layer is formed on the surface of the saidflexible band-shaped object, which is used as a base material. Theflexible band-shaped object is formed of a plastic film such aspolyethylene terephthalate (PET), polyethylene-2,6-naphthalate,cellulose diacetate, cellulose triacetate, cellulose acetate propionate,polyvinyl chloride, polyvinylidene chloride, polycarbonate, polyimide,and polyamide, or paper to which α-polyolefins with the number ofcarbons of 2 to 10 such as polyethylene, polypropylene, andethylene-butane copolymer is applied or laminated.

[0036] As the ferromagnetic powder used in the magnetic paint, variouskinds of materials can be used. When the ferromagnetic powder ishexagonal ferrite, particulates with a plate diameter not larger than 35nm and a plate ratio not lower than 2 can preferably be used, and whenthe ferromagnetic powder is ferromagnetic metallic powder, particulateswith a major axis length not longer than 60 nm and an axis ratio notlower than 2 can preferably be used. As for the particle size of theferromagnetic powder, particulates with an average primary particlevolume not higher than 10,000 nm³ can preferably be used.

[0037] As the solvent in which the ferromagnetic powder is soaked, asolution containing cyclohexanone is preferable. The content ofcyclohexanone is preferably 30 to 100% by weight of the total quantityof solvent. As a solution other than cyclohexanone, methyl ethyl ketone,toluene, butyl acetate, or the like is preferably used.

[0038] As a method for applying the magnetic paint, the roller coatingmethod, dip coating method, fountain coating method, etc. of applicationsystem, or the air knife coating method, blade coating method, barcoating method, etc. of metering system can be used. Also, as a methodin which the application system and the metering system are used in thesame portion, the extrusion coating method, slide bead coating method,curtain coating method, etc. can be used.

[0039] The thickness of the formed magnetic layer is preferably 0.02 to3 μm, further preferably 0.02 to 0.2 μm, in dry film. Also, the layerconstruction is preferably such that a nonmagnetic layer consistingmainly of nonmagnetic powder and a binder is provided between themagnetic layer and the nonmagnetic base material. In particular, aconstruction having a thin magnetic layer has an advantage that thedecrease in C/N in the shorter wavelength region is restrained not onlyto improve the performance of medium but also to enhance theproductivity because coating stripes can be reduced by the crushing ofagglomerated magnetic bodies.

[0040] The magnetic layer formed by applying the magnetic paint is driedafter being subjected to treatment for orientating the ferromagneticpowder, namely, the magnetic field orientation treatment. The driedmagnetic layer undergoes calendering treatment and hardening treatment,by which the magnetic tape material 20 is produced.

[0041] The magnetic tape material 20 thus produced is reeled out fromthe tape supply device 13, and is cut into a plurality of magnetic tapes26 by the slitter 14 while being transferred. The cut magnetic tape 26is wound up onto the tape winding-up device 50 after the magnetic layeris ground by the grinding apparatus 80. Although the grinding operationmay be performed on the wide magnetic tape material 20, it is generallyperformed on the magnetic tape 26 having been cut to a predeterminedproduct width (for example, 12.65 mm, 25.4 mm, 3.81 mm etc.)

[0042] The slitter 14 is an apparatus for cutting the wide band-shapedmagnetic tape material 20 into a plurality of magnetic tapes 26 by usinga pair of upper and lower rotating blades 32 and 30. As shown in FIG. 2,the slitter 14 is made up of a plurality of lower rotating blades 30, 30. . . each of which is formed into a roller shape as a backing blade anda plurality of upper rotating blades 32, 32 . . . of a thin disk shape,which cut the magnetic tape material 20 by giving a sheering force incombination with the lower rotating blade 30.

[0043] The lower rotating blades 30 are fittingly fixed to a lower shaft34 via spacers 36, and the upper rotating blades 32 are fittingly fixedto an upper shaft 38 parallel with the lower shaft 34 via spacers 40.The upper rotating blade 32 and the lower rotating blade are arranged sothat the blade edge portions thereof overlap with each other. The upperrotating blades 32 are urged to the right in the axial direction in FIG.2 by a spring, not shown, so that the blade edge portions of the upperrotating blades 32 are positioned in a state of being in contact withthe blade edge portions of the lower rotating blades 30. The upper andlower shafts 38 and 34 are connected to motors 41 and 43 capable offreely changing the rotational speed, respectively, so that thecircumferential speeds of the upper and lower rotating blades 32 and 30can be changed independently.

[0044] As shown in FIG. 1, between the supply reel 11 and the slitter14, there are provided a plurality of guide rollers 22, 22 . . . forforming a transfer path for the magnetic tape material 20 and a suctiondrum 24 for regulating the transfer speed of the magnetic tape material20. The suction drum 24 is connected to a motor (not shown) capable offreely changing the rotational speed, and is rotated in a state in whichthe magnetic tape material 20 is attracted to the peripheral surface ofthe suction drum 24, by which the transfer speed of the magnetic tapematerial 20 can be changed arbitrarily. The rotational speed of the hub18 (core) of the winding-up reel 17 in the tape winding-up device 50 iscontrolled on the basis of the circumferential speed of the suction drum24. The device which regulates the transfer speed of the magnetic tapematerial 20 is not limited to the suction drum 24, and a pinch rollerfor holdingly transferring the magnetic tape material 20 can also beused.

[0045] Between the slitter 14 and the tape winding-up device 50, thereare provided a plurality of guide rollers 22, 22 . . . for forming atransfer path for the magnetic tape 26 and the grinding apparatus 80with the cleaning device.

[0046] As shown in FIG. 3, the grinding apparatus 80 with the cleaningdevice mainly includes the diamond wheel 82 (grinding wheel) whichgrinds the magnetic layer of the magnetic tape 26 which is arrangedunder tension between tension rollers 28, 28, a rotating brush 84(cleaning device) which cleans a grindstone 83 of the diamond wheel 82,and a suction hood 86 surrounding the rotating brush 84.

[0047] As the diamond wheel 82, a diamond wheel of a metal bond type ispreferably used. Depending on the conditions, a diamond wheel of avitrified type, a diamond wheel of a resin bond type, or a diamond wheelof an electroformed type can also be used. The grain size of diamondabrasive grain used for the diamond wheel 82 is preferably #325 to#2000, further preferably #600 to #1200. If the grain diameter ofdiamond abrasive grain is too large, there undesirably arises a problemof flaws in magnetic layer. If the grain diameter of diamond abrasivegrain is too small, the grinding capability undesirably decreases.Regarding the bond material property, concentration, etc. of the diamondwheel, an appropriate value may be selected according to the compositionetc. of the magnetic layer. Also, regarding the winding angle and therelative speed in grinding, an appropriate value may be selectedaccording to the outside diameter of the diamond wheel 82, thecomposition of magnetic layer, etc. Therefore, the tension rollers 28,28 can be slid in the C-D direction in FIG. 3. The grinding operation isperformed by windingly applying the magnetic tape 26 through apredetermined winding angle to the rotating cylindrical diamond wheel 82so that the magnetic layer side is in contact with the diamond wheel 82and by applying a predetermined tension to the diamond wheel 82. Thewinding angle a of the magnetic tape 26 around the diamond wheel 82 ispreferably 60 to 150 degrees. In the example shown in FIG. 3, thedirection of rotation of the diamond wheel 82 is the clockwise directionso that the wheel surface moves in the direction reverse to the runningdirection of the magnetic tape 26. By this configuration, the relativespeed between the wheel surface and the surface of the magnetic tape 26can be made high.

[0048] The rotating brush 84 is provided on the opposite side to themagnetic tape 26 in contact with the diamond wheel 82, and also isprovided so as to be slidable in the A-B direction in FIG. 3 so that therotating brush 84 can be brought into contact with the diamond wheel 82at the time of cleaning. Thereby, the grindstone 83 of the diamond wheel82 can be cleaned at desired time during the grinding process. As amechanism for sliding the rotating brush 84, although not especiallyshown in the figure, a publicly known sliding mechanism can be used. Forexample, when the rotating brush 84 and the suction hood 86 areintegrated, there can be used a sliding mechanism in which the suctionhood 86 is slidably supported on a pillar rail via a nut member, and aball screw threadedly engaged with the nut member is rotated by a motorvia a speed reducer. Also, when the rotating brush 84 and the suctionhood 86 are separated, a sliding mechanism that is the same as describedabove may be provided on the rotating brush 84.

[0049] The material of a brush 84A of the rotating brush 84 ispreferably one of chemical fiber, animal fiber, and vegetable fiber. Abrush other than the above-described fibers, for example, a metal brushhas a problem in that it easily damages the grindstone 83, and hence theabrasive grains rather come off from the grindstone 83. Among thechemical fiber, animal fiber, and vegetable fiber, the chemical fiber isexcellent in wear resistance and heat resistance (the contact betweenthe brush of the rotating brush 84 and the grindstone 83 of the diamondwheel 82 produces heat), and thus it is suitable as the brush 84A of therotating brush 84. As the chemical fiber, nylon, acrylic, Teflon, etc.are suitable. Also, a brush produced by mixing a filler such as aluminumoxide with the chemical fiber is especially preferred.

[0050] The rotational speed of the rotating brush 84 is preferably inthe range of 100 to 1000 rpm. A cleaning force for removing loadedsubstances, which is loaded in the diamond wheel 82 by the grindingoperation of the magnetic layer of the magnetic tape 26, by the rotatingbrush 84 achieves an especially great effect when the rotational speedof the rotating brush 84 is in the range of 100 to 1000 rpm. Also, thedirection of rotation of the rotating brush 84 is preferably thedirection reverse to the direction of rotation of the diamond wheel 82.The reverse rotation increases a brushing force of the rotating brush 84with respect to the grindstone surface of the diamond wheel 82. Thebrush bristle diameter of the rotating brush 84 is preferably in therange of 0.01 to 0.3 mm. If the brush bristle diameter of the rotatingbrush 84 is too small, the stiffness is too low, so that a force forremoving the loaded substances adhering to the abrasive grain of thegrindstone 83 decreases, and also a force for scraping off the loadedsubstances intruding into concave portions in the grindstone 83decreases. If the brush bristle diameter of the rotating brush 84 is toolarge, the brush bristle becomes difficult to enter the concaveportions, so that the action of scraping off the loaded substances inthe concave portions decreases. Therefore, it is preferable that thebrush bristle diameter of the rotating brush 84 be further regulated inthe range of 0.01 to 0.3 mm according to the grain size of abrasivegrain used in the grindstone 83 of the diamond wheel 82. In the case ofa grindstone in which the grain size of abrasive grain is #600 to #1200,the brush bristle diameter of the rotating brush 84 is preferably in therange of 0.01 to 0.1 mm. Also, the brush bristle length of the rotatingbrush 84 is preferably in the range of 5 to 30 mm. The range of 5 to 30mm of the brush bristle length increases the cleaning force. It ispreferable that the brush 84A be pressed against the grindstone 83 undera pressure such that the amount of pressing of the brush 84A of therotating brush 84 against the grindstone 83 of the diamond wheel 82 isin the range of 1 to 5 mm. When the amount of pressing is in theabove-described range, the cleaning force is especially high. The amountof pressing can also be adjusted by the aforementioned slidingmechanism.

[0051] The suction hood 86 surrounding the rotating brush 84 is formedinto a cylindrical shape having a suction opening 88 on the diamondwheel 82 side, and the suction opening 88 is formed into a longrectangular shape in the axial direction of the rotating brush 84 (backand front direction of FIG. 3). The suction hood 86 is connected with apressuretight flexible tube 90, and is connected to a vacuum pump 94(refer to FIG. 1) via a trap device 92 (refer to FIG. 1). Thereby, whenthe vacuum pump 94 is operated, the interior of the suction hood 86 isevacuated, and thus air is sucked into the suction hood 86 through thesuction opening 88, so that the loaded substances having removed fromthe grindstone 83 of the diamond wheel 82 by brushing with the rotatingbrush 84 pass in the suction hood 86 and is sucked and recovered by thetrap device 92. In this case, since the suction hood 86 is in acylindrical shape, the loaded substances sucked into the suction hood 86are immediately exhausted through the flexible tube 90 without stayingin the suction hood 86. Therefore, the loaded substances having removedfrom the grindstone 83 are prevented from adhering again to the magnetictape 26. In this case, the suction pressure in the suction hood 86 ispreferably 1 to 5 kPa. If the suction pressure is lower than 1 kPa, theloaded substances having been removed from the grindstone 83 cannot besucked surely into the suction hood 86, and if the suction pressureexceeds 5 kPa, the suction pressure makes the transfer of the magnetictape 26 unstable, which exerts an adverse influence on the grindingoperation.

[0052] Next, the operation of the magnetic tape manufacturing system 10that is configured as described above will be explained.

[0053] First, the roll-shaped magnetic tape material 20 that has beenwound on the supply reel 11 of the magnetic tape manufacturing system 10is pulled out of the supply reel 11 continuously, and is transferred tothe slitter 14. The transferred magnetic tape material 20 is cut into aplurality of magnetic tapes 26 by the slitter 14, and each of themagnetic tapes 26 is transferred to the grinding apparatus 80.

[0054] In the grinding apparatus 80, the magnetic layer of the magnetictape 26 is ground by the diamond wheel 82, and at the same time, thegrindstone 83 of the diamond wheel 82 is cleaned by the rotating brush84 during the grinding operation. Thereby, since the grindstone 83 ofthe diamond wheel 82 can be cleaned during the grinding operation of themagnetic tape 26, the loading of the grindstone 83 can be eliminatedeffectively. Therefore, the grinding force of the diamond wheel 82 canbe stabilized, so that the variations in quality of the magnetic tape 26in the transfer direction of the magnetic tape 26 can be eliminated. Itis preferable that in this cleaning operation, the grindstone 83 of thediamond wheel 82 be always cleaned by the rotating brush 84 during thegrinding operation in which the magnetic layer of the magnetic tape 26is ground by the diamond wheel 82. Thereby, the grinding force of thediamond wheel 82 can be kept substantially constantly in a state of thegrinding force of a new diamond wheel 82 for a long period of time.Therefore, a higher-quality magnetic tape 26 having no variations inquality can be manufactured.

[0055] Next, the magnetic tape 26 having been ground in the grindingprocess is wound up onto the hub 18 of the winding-up reel 17. Thereby,for example, the magnetic tape material 20 is cut into 40 to 250magnetic tapes, and the magnetic tape 26 having a specified width (forexample, 12.65 mm, 25.4 mm, 3.81 mm, etc.) is manufactured.

[0056] The above is a description of an embodiment of the method formanufacturing a magnetic recording medium in accordance with the presentinvention. The present invention is not limited to the above-describedembodiment, and various modes of invention can be applied.

[0057] For example, the grindstone 83 of the diamond wheel 82 can becleaned intermittently with the rotating brush 84 during the grindingoperation of the magnetic tape 26. Further, cleaning can be performed ina time zone when the magnetic tape material 20 mounted on the tapesupply device 13 is exchanged.

EXAMPLES

[0058] Next, working examples of the present invention will be explainedby comparison with a comparative example. As the working example of thepresent invention, the magnetic tape manufacturing system 10 shown inFIG. 1 was used. As the comparative example, a manufacturing system inwhich the rotating brush 84 and the suction hood 86 are removed from thegrinding apparatus 80 of the magnetic tape manufacturing system 10 shownin FIG. 1 was used. The fabrication conditions were the same for theworking example and the comparative example, with the exception of thecleaning treatment.

[0059] The magnetic tape 26 was fabricated by being cut to a width of3.8 mm by the slitter 14 so as to conform to the DDS4 Standard. Therunning speed of the magnetic tape 26 was set at 200 m/min. The tensionof the magnetic tape 26 was controlled so as to be 100 g in the 3.8 mmwidth. The total thickness of the magnetic tape 26 was 5.6 μm.

[0060] The diamond wheel 82 used in grinding operation had a columnarshape, and the outside diameter thereof was 70 mm and the grain size ofabrasive grain was #800. The conditions in grinding operation werecontrolled so that the circumferential speed was 200 m/min. As a result,the relative speed between the diamond wheel 82 and the magnetic tape 26became 400 m/min. The winding angle α of the magnetic tape 26 around thediamond wheel 82 was set at 90 degrees.

[0061] As the rotating brush 84 used for cleaning, a rotating brushhaving the brush 84A whose material was nylon, whose brush bristlediameter was 0.1 mm, and whose brush bristle length was 10 mm was used.The rotating brush 84 was rotated at a rotational speed of 200 rpm, andwas set so that the amount of brush pressing was 3 mm. Also, the suctionpressure in the suction hood 86 was set at 3 kPa.

[0062] As a method for confirming the effects of the working example andcomparative example, an abrasion test was conducted using the magnetictape 26 thus manufactured. The configuration of the abrasion test isshown in FIG. 4. In this abrasion test, the magnetic tape 26 set undertension between guide rollers 98, 98 was reciprocatingly run so as to bepressed against an Alfesil bar 96, and the abrasion wear (μm) at the tipend of the Alfesil bar 96 was measured. The abrasion wear for satisfyingthe requirements of DDS4 Standard is 12 μm or smaller.

[0063] The Alfesil bar 96 is a bar made of an alloy of Al (aluminum), Fe(iron) and Si (silicon), and has a triangular prism shape. The runningspeed of the magnetic tape 26 was set at 300 mm/sec (18 m/min), thetension of the magnetic tape 26 was set at 20 g (in the 3.8 mm width),and the winding angle of the magnetic tape 26 around the Alfesil bar 96was set at 24 degrees. For the magnetic tape 26, a magnetic tape rollwith a length of 50 m was used.

[0064] The test results are shown in FIGS. 5A to 5C.

[0065]FIG. 5A shows the comparative example in which the rotating brush84 and the suction hood 86 were not provided. FIG. 5B shows workingexample 1, in which the grindstone 83 of the diamond wheel 82 wascleaned with the rotating brush 84 in a time zone when the magnetic tapematerial 20 mounted on the tape supply device 13 was exchanged. FIG. 5Cshows working example 2, in which the grindstone 83 of the diamond wheel82 was always cleaned with the rotating brush 84 during the grindingoperation in which the magnetic layer of the magnetic tape 26 is groundby the diamond wheel 82.

[0066] As the result, in the comparative example shown in FIG. 5A, theabrasion wear of the Alfesil bar 96 increased in proportion to thenumber of treated rolls of the magnetic tape material 20, and when thenumber of treated rolls reached three, the abrasion wear was 12 μm. Whenthe number of treated rolls reached four, the abrasion wear was 15 μm,deviating from the standard value.

[0067] Contrarily, in working example 1 shown in FIG. 5B, by grindingone roll of the magnetic tape material 20, the abrasion wear of theAlfesil bar 96 caused by the magnetic tape 26 was increased from about 4μm at the grinding operation start time to about 8 μm at the grindingoperation finish time. However, by cleaning the grindstone 83 of thediamond wheel 82 with the rotating brush 84 in a time zone when themagnetic tape material 20 was exchanged, the abrasion wear of theAlfesil bar 96 was decreased to about 4 μm.

[0068] In working example 2 shown in FIG. 5C, even if the number oftreated rolls of the magnetic tape material 20 reached ten, the abrasionwear of the Alfesil bar 96 could scarcely be detected, and the grindingforce of the diamond wheel 82 was kept substantially constant, beingalmost the same as the initial grinding force. Thus, it can be seen thatfor the tape 26 manufactured by performing the cleaning operation ofworking example 2 of the present invention, the abrasion of the Alfesilbar 96 scarcely occurs, and hence the grinding treatment of the magnetictape 26 is stable for a long period of time. In other words, it can beseen that the loading of the diamond wheel 82 decreases significantly,and hence the grinding capability of the diamond wheel 82 is stable fora long period of time. By the above-described abrasion test, theremarkable effects of the embodiment of the present invention could beconfirmed.

What is claimed is:
 1. A grinding apparatus comprising: a grinding wheelwhich continuously grinds the surface of a transferred web; and acleaning device additionally provided in close proximity of saidgrinding wheel, which cleans a grindstone of said grinding wheel.
 2. Thegrinding apparatus according to claim 1, wherein said web is a magneticrecording medium.
 3. The grinding apparatus according to claim 1,wherein said cleaning device is a rotating brush.
 4. The grindingapparatus according to claim 2, wherein said cleaning device is arotating brush.
 5. A method for manufacturing a magnetic recordingmedium, comprising the steps of: applying a magnetic coating containingferromagnetic powder and a binder onto a nonmagnetic band-shapedflexible base material to be transferred to form a magnetic layer; andgrinding said magnetic layer continuously with a grinding wheel on thedownstream side of transfer, wherein a cleaning device which cleans agrindstone of said grinding wheel is additionally provided in closeproximity of said grinding wheel to clean said grindstone during thegrinding operation.
 6. The method for manufacturing a magnetic recordingmedium according to claim 5, wherein the grindstone of said grindingwheel is always cleaned by said cleaning device during the grindingoperation in which said magnetic layer is ground by said grinding wheel.7. The method for manufacturing a magnetic recording medium according toclaim 5, wherein said cleaning device is a rotating brush which brushessaid grindstone.
 8. The method for manufacturing a magnetic recordingmedium according to claim 6, wherein said cleaning device is a rotatingbrush which brushes said grindstone.
 9. The method for manufacturing amagnetic recording medium according to claim 7, wherein the brushmaterial of said rotating brush is one of chemical fiber, animal fiber,and vegetable fiber.
 10. The method for manufacturing a magneticrecording medium according to claim 7, wherein the rotational speed ofsaid rotating brush is in the range of 100 to 1000 rpm.
 11. The methodfor manufacturing a magnetic recording medium according to claim 9,wherein the rotational speed of said rotating brush is in the range of100 to 1000 rpm.
 12. The method for manufacturing a magnetic recordingmedium according to claim 7, wherein the brush bristle diameter of saidrotating brush is in the range of 0.01 to 0.3 mm.
 13. The method formanufacturing a magnetic recording medium according to claim 9, whereinthe brush bristle diameter of said rotating brush is in the range of0.01 to 0.3 mm.
 14. The method for manufacturing a magnetic recordingmedium according to claim 10, wherein the brush bristle diameter of saidrotating brush is in the range of 0.01 to 0.3 mm.
 15. The method formanufacturing a magnetic recording medium according to claim 7, whereinthe brush bristle length of said rotating brush is in the range of 5 to30 mm.
 16. The method for manufacturing a magnetic recording mediumaccording to claim 9, wherein the brush bristle length of said rotatingbrush is in the range of 5 to 30 mm.
 17. The method for manufacturing amagnetic recording medium according to claim 10, wherein the brushbristle length of said rotating brush is in the range of 5 to 30 mm. 18.The method for manufacturing a magnetic recording medium according toclaim 12, wherein the brush bristle length of said rotating brush is inthe range of 5 to 30 mm.
 19. The method for manufacturing a magneticrecording medium according to claim 7, wherein the brush of saidrotating brush is pressed against the grindstone of said grinding wheelunder a pressure such that the amount of pressing of said brush againstsaid grindstone is in the range of 1 to 5 mm.
 20. The method formanufacturing a magnetic recording medium according to claim 7, whereinsaid rotating brush is covered with a suction hood having a suctionopening on the grinding wheel side.
 21. The method for manufacturing amagnetic recording medium according to claim 20, wherein the suctionpressure in said suction hood is 1 to 5 kPa.